1. Field of the Invention
The present invention relates to a control apparatus for a hydraulically operated vehicular transmission having a plurality of transmission trains to be established by a selecting operation of a plurality of hydraulic engaging elements. In this specification, the term "vehicular transmission" means a transmission for a vehicle such as a motor vehicle.
2. Description of the Related Art
As this kind of control apparatus, there has hitherto been known one in which solenoid valves are provided in a hydraulic oil circuit of a transmission and in which speed change is performed by controlling the solenoid valves by an electronic control circuit.
The electronic control circuit is constituted to perform an initialization operation at the time of starting up and, after the completion of the initialization operation, to perform an in-gear control (i.e., a control of gear-in or of gear engagement) and a speed change control based on signals from various sensors. Then, even when the electronic control circuit temporarily fails due to voltage drop or the like while the vehicle is running, the electronic control circuit is started with the recovery of the voltage and the initialization operation is performed.
In a neutral range, supply of hydraulic oil to all the hydraulic engaging elements is stopped by a manual valve, whereby the transmission becomes a neutral condition. In a running range, on the other hand, hydraulic oil is supplied to any one of the hydraulic engaging elements via the manual valve and shift valves, whereby any one of the speed stages is established. In this case, if a low speed stage is established while the vehicle is running at a high speed, there will occur an overrotation (excessive rotation) of an engine. As a solution, in the conventional apparatus, the following arrangement is made. Namely, during the initialization operation of the electronic control circuit, a signal to establish a high speed stage is outputted. After the completion of the initialization operation, if the detected range is the running range, speed change is performed to a speed stage depending on the vehicle speed at that time.
In the above-described conventional system, when the electronic control circuit is re-started after a temporary failure while the vehicle is running at a low speed in the running range, a high speed stage is established during the initialization operation, and thereafter downshifting to a low speed stage is performed. Therefore, the downshifting to a lower speed stage is performed after the rotational speed of the engine has once been lowered. As a result, it becomes necessary to largely increase the rotational speed of the engine at the time of downshifting. The time required for the downshifting thus becomes long, and it takes time before a driving force desired by a driver can be obtained.
In view of the above point, the present invention has an object of providing a control apparatus in which, after a failure of the electronic control circuit during running, the driving force can be recovered by re-starting at an early time.